i) Field of the Invention
The present invention relates to a navigation system mounted to a vehicle for guiding a vehicle such as a car according to a predetermined route, and more particularly to a vehicle navigation system to orally inform a driver of a route to be selected.
ii) Description of the Related Art
Conventionally, in order to reduce a driver's load, a variety of devices have been proposed and mounted to a vehicle and a navigation system for guiding a vehicle to a destination along a route is known. In this navigation system, when the vehicle passes through a branch point such as an intersection, a route to be selected is advised to a driver. In an example of a navigation system put to a practical use, an image display device using a display is provided on an instrument panel of the vehicle and a route is advised to the driver.
In addition to the information by the image display, another navigation system for issuing route information orally has been known. For example, as disclosed in Japanese Patent Laid-Open No. Sho 62-267900, in a navigation system, when the vehicle has reached a predetermined position (30 m) before an intersection, in order to advise route information, an indication is given to the driver orally. In such a navigation system using a voice, there is no need for the driver to look at a display and he can concentrate on looking ahead.
In the route guiding system of the prior art, however, oral route guidance is issued only with respect to right-turns and left-turns at crossroads, but not to driving straight or adjacent roads. Toll roads, express highways and motorways have many entries along the roads, rather than intersecting points. Therefore, no oral route guidance is issued for such roads. This may puzzle many drivers.
Particularly, if the entry into a toll road or the like is located adjacent to the general road, a driver may become puzzled without route guidance.